It is known in the prior art to print on light sensitive media using a liquid crystal display as a shutter. Typically, the image bearing surface of a liquid crystal display (LCD) is optically focused onto a sheet bearing a light sensitive emulsion. A source of light is provided behind the LCD to illuminate an image on the surface of the LCD. When color images are being produced, the media supports 3 types of color-sensitive chemistries that form the color image. Prior art discloses the use of a display to create color images using a monochrome LCD and various colors of light. The monochrome LCD is sequentially loaded with separated color planes of a source image, and the corresponding light is used to illuminate a color printing media.
U.S. Pat. No. 4,811,089 discloses the use of a linear electrostatic head or ink jet head to write separate color records to masks. Red, green and blue light sources are then used to illuminate each of the three color masks to expose color-sensitive media.
U.S. Pat. No. 4,935,820 uses a white light source to illuminate a LCD. The LCD carries color separate information, and a dichroic mirror is used to provide the appropriate light color for each separation. Because the dichroic mirror absorbs the other two unused portions of the white light, the system is energy inefficient. U.S. Pat. No. 4,935,820 is used to expose media with very low light sensitivity, which is stated as " . . . in the range of 103 ergs/c.sup.2 to 107 ergs/cm.sup.2." Such a media requires a very high output light source such as " . . . a 220 watt Tin Halide Arc Lamp type SN 220 manufactured by Phillips." In addition, the LCD should be a highly efficient source of light images.
In commonly assigned U.S. patent application Ser. No. 08/703,289 filed Aug. 26, 1996 to McIntyre et al, there is disclosed apparatus for using a color LCD on the back of electronic cameras to write images to light sensitive media. Such displays have separate pixels for each color. Creating an image on a digital display using separate color elements creates images inferior to images having all three colors of light emitted from common pixels. U.S. Pat. No. 5,337,068 discloses the use of a monochrome LCD, and a multiple sets of red, green and blue lamps to create color images on the monochrome display. Separate color information is written to multiple areas simultaneously at a rapid rate to project all three colors through common pixels. Appropriate lamps are activated simultaneously in separate areas as data are written to each area. Multiple lamps are required for each color of the separate areas and multiple lamps are energized simultaneously during display.
Prior art uses large, high power illumination systems to write separated color images to light sensitive media using liquid crystal displays. It would be useful to create a simple, low-cost, small, low-energy illuminations system to print images without color filter array artifacts. Such a printer could be battery powered and portable.